Light-induced degradation of a-Si solar cells is dependent on their design. The degradation rate for single cells increases with i-layer thickness. Very thin i-layer devices (d < 100 nm) exhibit a delayed onset of degradation which is accompanied by a severe loss of open circuit voltage at prolonged exposure times. By extrapolating i-layer thickness to zero and therefore separating bulk and interface effects, the latter may account for a substantial loss of stability. The introduction of a SiC buffer layer at the p/i interface results in a considerable higher degradation mainly caused by a loss in fill factor.
Double stacked cells, as compared to single cells having similar initial efficiences, show higher stability. The instability at extended exposure times of very thin single cells as used in a tandem configuration did not influence the stacked device.